1. Field of the Invention
The present invention disclosed herein relates to a semiconductor devices and methods of fabricating semiconductor devices. More particularly, the invention relates to nonvolatile memory devices and methods of fabricating nonvolatile memory devices.
2. Description of the Related Art
As semiconductor devices are becoming more integrated, line-widths of patterns constituting the semiconductor devices are decreasing. The patterns may be conductive patterns including gate patterns and lines. The reduction of line-widths of the conductive patterns leads to an increase in electrical resistance and resistance-capacitance (RC) delay. Accordingly, technology has been proposed to form the gate patterns with a metallic material having a low specific resistance. For example, the gate patterns may be formed of tungsten (W) having a specific resistance of 5.5×10−8 Ωm. Meanwhile, tungsten silicide (WSix) including tungsten has a specific resistance in the range of 3×10−7 Ωm to 7×10−7 Ωm. Polysilicon has a specific resistance of 10−5 Ωm and thus, the specific resistance of the tungsten silicide is several tens of times smaller than that of polysilicon.
Although tungsten has a low specific resistance, reliability of the gate insulating layer is degraded when a tungsten layer is directly in contact with a gate insulating layer. Therefore, a semiconductor layer may be interposed between the tungsten layer and the gate insulating layer. The semiconductor layer may be a polysilicon layer. In addition, a barrier metal layer may be disposed between the tungsten layer and the semiconductor layer. The barrier metal layer may play a role in reducing and/or preventing the interfacial reaction and mutual diffusion between the semiconductor layer and the tungsten layer. Generally, the barrier metal layer may be a metal nitride layer including a tungsten nitride (WN) layer and a titanium nitride (TiN) layer. However, when the metal nitride layer is directly in contact with the semiconductor layer, the contact resistance may be increased, which may lead to considerable problems in operational characteristics of the semiconductor device.